How To Size Activated Carbon Filter

By Robert J. Potwora

Activated carbon (AC) is a universal adsorbent. It is used to purify the h2o we drinkable, the air nosotros exhale, many of the foods nosotros eat and numerous industrial chemicals that we use every day. In drinking h2o handling, AC is used to remove taste and odor, VOCs and a myriad of unwanted organic materials. Us EPA lists granular activated carbon (GAC) equally a best available technology (BAT) to remove specific organics from drinking water. In domicile water filtration devices, it is likewise used to remove disinfectants such as chlorine and chloramines, every bit well equally DBPs.

Activated carbon types
The three almost common types of raw materials used to make Air-conditioning are coal, coconut shell and wood. Other types of raw materials are used to a much lesser extent, including fruit and olive pits, nut shells, bamboo and rice hulls. The most mutual types of AC used for water handling are coal-, coconut- and wood-based. Activated carbon tin can be used in powdered form (PAC), in granular course (GAC) or in pellet form, known equally extruded activated carbon (EAC). Powdered activated carbon is dosed into the water and then filtered out. Granular activated carbon and, to a lesser extent, EAC, is used in fixed-bed-adsorber columns.

For small POU Ac systems, such as faucet mounted and pitcher devices, 20 x 50 mesh size GAC is preferred. This small-scale size provides fast kinetics for adsorption of impurities and chlorine removal, while maintaining an adequate force per unit area drop. Larger POE systems employ 12 ten 30 or 12 x 40 mesh size. This larger particle size still allows for fast kinetics and an acceptable force per unit area drop, while more easily covering a large area. Both forms of GAC and EAC tin be thermally reactivated after they are spent, whether for cost savings or for ecological benefits and waste product minimization.

Drinking water treatment
The drinking h2o segment is conspicuously 1 of the largest uses of Air-conditioning using PAC and GAC. Several hundred-million pounds of Air-conditioning are used annually in the US. Likewise the ever-increasing demand to clean drinking h2o, a newer marketplace driver is The states EPA's last implementation of the DBP rules. These regulations are designed to help prevent the formation of hazardous compounds, such as trihalomethane (THM) and haloacetic acids (HAAs), and past removing organics from municipal drinking water supplies earlier chlorine or chloramines are added as disinfectants. An estimated 50 to 70 meg pounds/yr of GAC are currently needed for this market segment and these regulatory drivers are expected to provide tremendous growth for the Air-conditioning market place in the time to come.

Another growing area of business is in the use of AC to remove trace amounts of pharmaceuticals and personal care products (PPCPs), as well as endocrine disrupting compounds (EDCs) from drinking h2o. Many adverse ecological effects accept been attributed to these chemicals, simply it is non yet clear what risks they pose to human being health. Previously, the presence of these chemicals in water was known but was difficult to quantify. Today, new analytical methods can quantify the presence of these chemicals down to the number of parts per trillion (ppt). One part per trillion is equal to i drib in 26 Olympic-sized swimming pools.

The overwhelming bulk of EDCs and PPCPs are not currently regulated and the levels constitute in drinking water are usually very depression. Human wellness risks associated with these low levels, however, are non yet fully understood. Since conventional municipal water treatment does non remove ppt levels of these chemicals very well, POE and POU water handling devices with Air conditioning can help fill this void. A new drinking water standard, NSF/ANSI 401, was recently developed to evaluate the performance of POE/POU devices on these potential contaminants.

Fine-mesh activated carbons and carbon blocks
Kinetically, the adsorption rate of organic impurities and the dechlorination rate of ACs goes up speedily every bit the particle size goes down. This kinetic issue is utilized in making carbon blocks for POU and POE markets. Carbon blocks are manufactured from so-called fine-mesh AC that are typically 10 to 15 times smaller in particle size than the GAC used in municipal water filters.

Typical fine-mesh sizes include xxx 10 200, 50 x 200 and 80 ten 325. The fine-mesh Ac is molded or extruded with binders to form a solid block. Additives may as well be incorporated into the carbon block to target certain contaminants such every bit lead and to enhance performance. The carbon cake filters typically have a 0.25- to 1-inch (half dozen.35- to 25.4-mm) cake thickness and accept an empty bed contact time of only seconds, as compared to the minutes of contact time required for effective contaminant removal with GAC.

One of the more common uses of AC is for the removal of chlorine to ameliorate the taste and odor of chlorinated drinking water. Equally the particle size of the AC is reduced, chlorine-removal life of the Ac filter is dramatically increased. For instance, a filter containing 150-cubic centimeters of a 12 10 40 mesh size Air-conditioning has a capacity of fourscore gallons (302 liters). For the same book of Air conditioning, reducing the carbon particle size to 100 ten 200 mesh increases the bed life to 10,000 gallons (37,854 liters).

Precise particle size command

As smaller and smaller Ac particles are used to make carbon blocks, the demand for precise particle size control becomes more important. Small variations in carbon particle size can have a meaning impact on water flowrate and contaminant removal functioning. To illustrate, three examples of particle size distribution (Types A, B and C) are shown in Table i. Type A shows an example of coarser particle size and narrower distribution. This leads to carbon blocks that produce a higher flowrate of > 4.0 liter/min, but a relatively depression efficiency of contaminant removal. At the other cease, Type C shows an instance of finer particle size and wider distribution. This leads to carbon blocks that produce a lower flowrate of < 2.5 liter/min, but a relatively high efficiency of contaminant removal. In betwixt, Type B shows an instance of optimal particle size distribution with precise control. This leads to carbon blocks that produce the desired flowrate of 3.5 to 4.0 liter/min, while maintaining a loftier efficiency of contaminant removal.

To accomplish the optimal particle size distribution, precise particle size measurements are needed. (Traditional sieving methods originally adult for GAC were institute unsatisfactory for fine-mesh carbon.) Modern instruments are based on laser diffraction. Such instruments can deliver rapid, authentic particle size distributions for both wet and dry dispersions with a minimum of effort over the nanometer to millimeter particle size ranges.

Decision
In that location are many dissimilar types of Ac available. Selecting the right type and the right particle size distribution is disquisitional to ensure proper performance. Work closely with your supplier to ensure that you lot select the most economical AC to come across your performance objectives.

About the writer
Robert J. Potwora, of Oxbow Carbon LLC, has over thirty years experience in the activated carbon industry. He is too Chairman of ASTM'southward Commission D28 on Activated Carbon. Potwora may be reached past phone (760) 630-5724 or email robert.potwora@oxbow.com.

Nigh the company
West Palm Beach, FL-based Oxbow Activated Carbon LLC, one of the largest private Us companies, provides 1 of the most diverse lines of AC solutions backed by skillful technical support and knowledgeable customer service. The company has advanced processing capabilities in N America and Europe with direct sales and distribution operations around the world. Oxbow is the earth's leading marketer, upgrader and benefactor of petroleum coke, calcined petcoke and sulphur products. The company'southward calibration, expertise and leading market positions take immune it to create a powerful global sourcing platform with superior market intelligence and longstanding relationships with its key suppliers and customers. Oxbow activated carbon has greatly benefited from its ability to leverage Oxbow's global operations and extensive global distribution network. The visitor's website is www.oxbowactivatedcarbon.com.